Silver halide photographic materials are broadly utilized in various fields of, for example, photoengraving processing and medical diagnosis. With widening application of these materials, the demand for development and processing for photographic image formation is increasing and, in particular, rapid and stable development of photographic materials is strongly desired.
After exposure, a silver halide photographic material is generally processed by processing steps including development, fixation and rinsing with water. A black-and-white developer for the process is generally an alkaline solution containing a hydroquinone compound as a developing agent, an aminophenol or 3-pyrazolidone compound as an auxiliary developing agent and sulfite ions.
The sulfite ions are used in the form of a sulfite or bisulfite of an alkali metal, and it has been an indispensable component for maintaining the developing activity of hydroquinone compounds and for inhibiting aerial oxidation of the developer. In addition, since the sulfite ions have an activity of suitably dissolving silver halides, it is often used for improving the graininess of photographic materials by positively utilizing its action of solution physical development in the development reaction step.
On the other hand, a developer having a higher stability (preservability) is desired. A developer that is stable over a long period of time to aerial oxidation requires less labor for its maintenance and charging to the processing system, and reliably provides constant photographic performance. In particular, where the developer composition is to be constantly maintained and controlled in an automatic developing machine with a predetermined amount of a replenisher being added thereto, the stability of the developer is important for reducing the amount of the replenisher and operational cost. In order to reduce the amount of the replenisher, the stability of the developer must be improved. This is because reduction in the amount of the replenisher correspondingly increases the residence time of the developer in an automatic developing machine and also in the replenisher tank, to thereby expose the developer to a greater degree of aerial oxidation.
Aerial oxidation of a developer may be prevented by increasing the sulfite concentration of the developer, but there is a limit to increasing the sulfite concentration, The reasons are as follows. First, in general, a concentrated developer stock is diluted before use for actual development, and an important factor in adjusting the concentration of the concentrated developer stock is the sulfite content. If a large amount of a sulfite is added to a developer so as to elevate stability of the same, the concentration of the developer stock must be concurrently reduced. In an extreme case, the concentration of the initially prepared developer stock is the same as that of the developer actually used in an automatic developing machine. In other words, the volume of the developer stock is the same as that of the latter developer for actual use in the machine. This result is disadvantageous in view of the transportation cost and the space for the developer. Second, because a developer containing a large amount of a sulfite dissolve much of the silver halide of the silver halide photographic material being processed, the dissolved silver tends to stain the development racks and rollers.
Because of these reasons, incorporation of sulfite in large quality into a developer is limitative, although the sulfite effectively stabilize the developer. Therefore, there is a need for further improvement of the stability and preservability of a developer.
Ascorbic acid is known as a chemical additive capable of improving the preservability of a developer. For example, JP-B 44-28673 (the term "JP-B" as used herein means an "examined Japanese patent publication") describes a known technique of adding ascorbic acid to a lith developer. However, ascorbic acid involves some drawbacks. A deteriorated ascorbic acid in a developer lowers the pH value of the developer, and ascorbic acid is easily decomposed in a developer especially in the presence of a metal ion such as copper ion or iron ion.
The use of ascorbic acid derivatives is also known. Other examples of the use of ascorbic acid derivatives in this technical include U.S. Pat. No. 2,688,549 and JP-B 36-17599 which describe use of ascorbic acid for activation of development and improvement of gradation, and also as a preservative for 3-pyrazolidones. In fact, ascorbic acid has been found to be effective in preventing aerial oxidation of a developer. However, use the compound disadvantageously involves lowering the pH value of a developer, which in turn lowers the developing activity thereof.